Rotary blower and pump



Aug. 11, 1931. I- L W. SWARTWOUT 6 ROTARY BLOWER AND PUMP Filed Sept. 15. 1927 3 Sheets-Sheet, 1

3 a A 5 0/ 4 g 5 d mmawwmmm a W W 0 1 4% w E a, 1- w 9 2 Aug. 11, 1931. E. w. SWARTWOUT ROTARYIBLOWER AND PUMP Filed Sept. 13, 1927 5 Sheets-Sheet. 2

Aug. 11, 1931. E. w. SWARTWOUT 1,813,767

ROTARY BLOWER AND f UMP Filed Spt. 13. 1921 :5 Sheets-Sheet. 5

Swoamtoz Patented-Aug. 11, 1931 EVERETT W. SWARTWOUT, 01 WHITE PLAINS, NEW YORK ROTARY BiowER AND rumr Application filed September 13, 1927. Serial No. 219,225.

My invention relates to rotary blowers and pumps.

More particularly, my invention relates to rotary blowers and pumps taking at the suc- 5 tion side air, gases, or liquids, either singly or as mixtures,- and which deliver against a desired differential pressure with improved pressure regulation at any operating speed, with variable capacity when operating at any constant speed and with improved efliciency. According to the prior act, the principal advantages of machines or rotary blowers and pumps of that type in which there are two parallel shafts carryingmating lobed impellers in a cylinder, are that the capacity per revolution is constant after the losses due to slip at the various operating pressures have been deducted; that the total net capa city is large; and that no lubrication within the cylinder is required and therefore deliverlng a product which is unpolluted by oil. The disadvantages of these prior types are that the efficient compression range is limited to small differential pressures due to the fact a 5 that a compression of air, or the fluid or other medium being compressed, what is termed instantaneous compression, is brought about b the return flow of the medium from the elivery line at the delivery line pressure back into the cylinders of the unit. Such return flow produces a hammer blow on the impellers immediately upon the impellers making a communication between the delivery line'and the compartment in '35 the impeller cylinder containing the medium tobe compressed for delivery, thus causing a periodic momentary tendency to reverse the direction "of rotation of the impellers and resulting in the uneven wearing of the oper- 40 ating andtiming gears, and giving rise to contlnuously increasing noise of the gears,-

and finally effecting incidental damages re:

sulting from the improper timing of the impellers'and causing them to strike and wear,

accompanied by decreased efliciency due to 1 er slip or leakage from the deliver the larger clearances and consequently greaits1 0 back to the suctionside, heating at t e suction with relatively high temperature at the delivery pressure, heating up of the machine, in reduction in the net capacity of the machine,

and other mechanical disturbances due to the expansion of some parts more than others due to the progressively increasing tempera- 4 ture of the medium at the suction side and II within the machine. v

In machines of the prior typeemploying instantaneous compression, the full diflerential pressure is continuously across the machine which gives rise to a substantial slip, 00 or leakage from the high pressure side to the lbw pressure side of the machine, resulting in reduced volumetric efiiciency, loss of capacity and reduced overall efiiciency. When operated at constant speed and with constant differential pressure, the delivered capacity of machines of the prior type may only be varied-by wasting the unwanted .compressed air by relieving1 it into the atmosphere, or by expandingt e excess compressed gas from the delivery side of the machine back tothe suction side of the machine through a throttling valve controlled by a dlaphragm pressure regulator or the like, causing heating at the suction side and saying no power as compared with that required when the machine is operated at full delivered capacit :A ccording to my invention, I employ rotary machines of any type, but preferably of that type having two parallel shafts carrying mating lobed impellers in a cylinder, comprising variable capacity means by what is termed unloading during periods whenmore of the compressed medium is delivered than is wanted or needed to' maintain asubstan tially constant delivery pressure; Means are also provided for checking and preventing tion side of the machine, means for interconnecting and disconnecting the suction and delivery sides of the machine prior to the delivery pipe so that only periodically, or 5 continually as needed, the medium is being compressed and delivered against the delivery pressure. When unloaded, the medium is not compressed at all but is merely circulated through the machine and back to the suction side at the suction pressure, therefore requiring no work and thus increasing the efliciency and reducing the total power required by the machine. in proportion to the time unloaded and the time of periodically compressing the delivering.

To further improve the volumetric efliciency, to improve the efficiency of compression, to produce smooth operation at high speeds, and for the purpose of expanding the commercial uses for machines of the rotary type, I provide means for producing substantially gradual or adiabatic compression which eliminates the popping back into the machine and the other disadvantages incidental to in stantaneous compression and which makes machines adapted for efficient operation at relatively high diflerential pressures. According to my invention, the compressed medium is held in the delivery pipe after it is delivered and is precluded from rushing back into the machine; furthermore, the full delivery pressure is attained by gradually increasing compression within the cylinder and the full delivery pressure is impressed upon the compressing elements of the machine only during a relatively short portion of each cycle from the suction side to the delivery side,

thereby reducing the slip or leakage through the machine, as this is a function of the differential pressure and time. According to my invention machines are provided which are not only well adapted, but highly eflicient, when used as vacuum pumps or as gas boosters operating with relatively high differential and high ratio of compression.

Though many new and useful applications of my invention will be perceived by those skilled in the art, my invention is especially useful and advantageous to the manufactured gas industry. One application of my invention is in the pumping of manufactured gas at variable rates to supply the fluctuating demands of various communities, utilizing as motors for driving these gas pumps, electric motors of the standard constant speed squlrrel cage induction type. Motors of this type are especially valuable in that they do not cause sparking, and therefore the danger of explosions is eliminated. By the use of 60 directly connected motor driven gas pumps operated at constant speed, the capacity may be varied to suit the needs, much power is saved, and should the electric power supply suddenly fail, a reverse flow of the gas is pre- 65 vented and the gas pumps are protected from being rotated in the reverse direction as gas motors at excessively high speeds.

The accompanying drawings show certain representative embodiments of my inven-. tion. The principles may be applied to compressors, blowers and pumps of types ditfering from the specific type illustrated and variations may be made without departing from the principles of the invention, as comprehended in the scope of the appended claims.

Fig. 1 is a diagram of three compresslon cycles.

Fig. 2 is a. vertical central section of Fig. 3, illustrating a simplified form of my invention;

Fig. 2a is a sectional elevation on line 2a2a of Fig. 2.

Fig. 3 is a side elevation of Fig. 2.

Fig. 4: is a vertical central sectional elevation of a complete assembly, embodying my invention.

Referring to Fig. 1, the diagram, abccl, represents a pressure volume cycle of the ideal adiabatic character as will be understood by those skilled in the art. The diagram, abegficd, represents a pressure volume cycle of the instantaneous compression character and which is the cycle which characterizes the operation of positive pressure lobed impeller type of unit as constructed according to the prior art. The diagram, abefcd represents a pressure volume cycle of approximate adiabatic form and which is the compression cycle obtained when operating machines ac- 100 cording to my invention. It will be understood th'at when pumping liquids which are devoid of compressible gases, the pressure volume representation will be of the rectangular form with qualification, as will be under- 105 stood. It is also understood that the elliciencies of the respective cycles, and also the power input of machines operating on these respective cycles, are in proportion to the areas of the respective compression cycles.

In the adiabatic cycle, abcd, the period of gradual compression takes place under the portion of the diagram represented by the curved line, 60, and the period or relative length of time during which delivery occurs 115 against the delivery pressure is represented by the length of the line, col.

In the positive pressure instantaneous compression cycle, abegfcd, compression is instantly effected by the rushing back of the 120 gas from the delivery side at the delivery. or discharge pressure, into the compression com partments of the machine, as is represented by the line, beg, of the diagram, abcgfcd. The relative length of time at which the delivery 125 pressure is across the machine, and the time during which slip, or leakage due to the full difierential pressure occurs, is represented by the length of the line, gfcd, of the diagram, abegfcd.

According to my invention, when compressing ,gas'free from condensed liquid, there may be a slight instantaneous compression caused by thepopping over of the compressed gas left in the compression compartment, after delivery into the discharge has ceased, into the compartment on the suction side of the machine filled with gas at inlet pressure,

- thus slightly increasing the pressure of the.

ration of time represented by the length of the line, fad, of the diagram, abefcd. It will be understood that when a considerable quantity of condensed liquid is present in the gas, as when handling mixtures of gas and liquor such as is encountered in the operation of filter presses and the like, enough of the liquor will continuously remain in the machine over the impellers to seal them against leakage .and to cause whatever gas is present in the mixture to be compressed sole- 1y according to the adiabatic compression cycle, thus improving the power consumption and the efliciency of these machines considerably when compared with'machine's oi the prior art types.

When complete unloading is effected as provided for in my invention, machines of any type will merely continuously 'circulate gas at the suction pressure, or liquld in any proportion, from the suction side of the machine through'the machine and its discharge chamber back to the suction side, and such cycle is repeated duringthe time when so unloaded; such cycle is represented by the line, ab, of the three superimposed cycles represented by the diagrams of Fig. 1. h

Referring to Fig. 2, the impellers 1, 2, shown in cross section, are mounted upon their respective shafts 3, 4. The impellers may be made according to any curved form such as the involute, the cycloidal, or other curves which maketheir lobes interengage mesh and mate in their various angular relationships with each other when rotated in opposite directions on parallel shafts, without contact between the impellers or with the surrounding casing, clearances. Though the impellers 1, 2 are preferably shrunk onto the shafts '3, 4 the keys 5, 6 may be employed to insure rigid relationship between the respective impellers andshafts. Thecasing comprises two heads at the respective ends of the cylinder. The cylinder may be made solid, or may be divided into halves, split horizontally along the lines 7, 8, thus making the cylinder quarter 12, which are given rigidity sections 9, 10, 11,

but-with relatively small I by the ribs 13, 14, 15, 16, respectively; The ar row 19 shows the direction of rotation of the impeller 1 and the arrow 20 shows the direction of rotation of the impeller 2. The line 21 of the'cylinder section 9, and the line 22 of the cylinder section 11 shows the lines at which the impellers 1, 2 close the suction side of the medium to be handled. The line 23 of the delivery compartment 24 shows the com- I mon line past which the impellers 1, 2 sweep. The impellers '1, 2 are driven and maintained in timing relation by the pair of gears 25, 26. The volume 27 formed between the impellers 1, 2, the cylinder section 10 and the delivery compartment 24 is what isleft following delivery from the delivery compartment and is the volume of gas at the delivery pressure which is mixed with the volume of gas 28 at the inlet pressure formed between the impeller 2 and the cylinder sections 11, 12 and the delivery compartment 24. Upon rotation of the impellers 1,-2, beyond their positions as shown in Fig. 2, the impeller 2 will pass the line 23 thus making communication between the volumes 27 and 28, and initiate compression adiabatically of the enclosed gas. It will be noted that the impeller 2 rotates from the line 22 of the cylinder section 11 to the line 29 of the section llwithno differential pressure between the suctidn opening and the gas volume 28 and therefore,

there is no slip past the impeller 2 and the cylinder section 11 while rotating from the line 22 to the line 29. 'A corresponding region of no slip occurs in the rotating of the impeller along the wall of the cylinder section 9 beginning at the line 21.

As appears in Figs; 2 and 2a, the port of thedelivery compartment 24 is provided with a valve constructed to pass air, gas or other medium in one direction solely. Preferably, thedelivery compartment for a two lobe impeller is provided with two sets 30, 31 of such'uni-directional valves, comprising the spaced slots 30a of the valve 30, arranged in alternate spaced relation with respect to the slots 30?), the valve strips 300 being disposed to be displaced in one direction only relative to the discharge openings of the slots 305, or the equivalent whereby upon the pressure in the delivery compartment ing-the pressure in the delivery line 23, each valve 300 is moved in its slot 30?): to effect communication through the valve slots. Like compartment is provided with the respective openings 32, 33 and comprises the centralabutment having the arcuate face-s 23a, 23b

and further comprises the arcuate faces 21a, 22a, co-operating with the respective impellers 1, 2, thereby forming compression chambers between the respective impellers m tive lobes approach the delivery substantially no compression of the gas takes place.

Pursuant to my invention, arcuate extensions 21a23a and 22w23b,see Fig. 2, of the walls of the cylinder meet at or near the common line 23 and thus co-operate with the respective impellers to form spaces for the delivery of the gas without extending the dlmensionsof the cylinder, and serving also to prevent the return of the gas previously 0 compressed and delivered into the delivery line. My invention provides the further coacting means in the form of uni-directional valves, opening outwardly of the casing into the delivery line, whereby the distinctive characteristics graphically depicted in the pressure-volume diagram of Fig. 1 are attained; structurally stated, my improved machine comprises essentially a pump or compressor capable of sucking in at inlet pressure the volume ab, succeeding which is a partial compression period in which the pressure of the gas is suddenly increased solely and wholly within the compressor along line be, after which the gas is adiabatically compressed along the line 6}, following which the compressed gas is delivered into the discharge line for the volume fd, at the discharge pressure represented by the line ad.

In prior types and uses of inter-engaging lobed impellers the work required on compression-which is of sudden compressionis represented on the diagram Fig. 1 at abegfod. In this diagram the gas is sucked 5 into the machine in a volume and at an inlet pressure represented by the line ab. At the point I), the tips of the respective impellers pass the cylinder at the points 21a, 22a, respectively, thus permitting the discharge line pressure to shoot back into the compartment opened by the respective movements of the two impellers. This causes the pressure which was formerly at the suction pressure to instantly arise along the line bego until the discharge line pressure immediately becomes the pressure in these compartments, whereby the discharge line pressure therefore compresses the gas which was present at the Suction pressure. After this the'co-operating movement of the two impellers delivers the compressed gas into the discharge line along the line gfccl at the pressure (la.

As distinguished from-piston pump machines orcompressor, the movement of each piston :of a multiple piston machine in one the pressure within the cylinder is at the suc- I tion pressure, and as there are discharge valves which prevent communication be tween the discharge pipe and the interior of the cylinder, the gas in the cylinder is gradually or adiabatically compressed along the curve 720, until the pressure within the cylinder is slightly greater than the delivery pressure, thus overcoming the resistance of the delivery pressure against the spring valves and overcoming the frictional resistances of these valves. The compressed air is then delivered for the volume 012, at a pressure ad, after which the cycle is repeated.

After the gas has been adiabatically compressed it is deliveredthrough the valves 30, 31, the ports 32, 33 and the valve bonnets 34, 35 of the delivery'compartment 24. When the requirements are for compressed gas at constant capacity, the discharge line is connected directly with the delivery compartment 24, as at the flange 36, while if a bypass of any kind is desired, it may be connected with the delivery compartment 24 as at the flange 37. Thus, it will be noted, that whatever medium is delivered from the volumes 27, 28 into the delivery compartment 24 there is no slip back into the machine, and, also, all of the medium taken in at the suction side, excepting 'the slip, is positively delivered into the delivery compartment 24, re-

sulting in high volumetric efficiency and low 7 power consumption.

Referring to Fig. 3, like numerals designate like parts as are illustrated and-described in Fig. 2. The bottom head section 38 and the bottom head section 39 are attached to I the respective ends of the cylinder section, 9, 11. The top head plate sections'40, 41 are attached to the bottom head sections 38, 39, and to the cylinder sections 10, 12. The bearings 42, of which two are shown, are supported in the head-plate 38, while the bearings 43, two in number, are supported by the headplate section 39. The two dupli- 1 cate, intermeshing, synchronizing and timing gears 25, 26, respectively, are respectively mounted upon the shafts 3, 4 and are disposed within the housing 45, preferably remote from the cylinder, so that the gears can be fully protected from dust and dirt and run in a bath of oil, to maintain the impellers 1, 2 in proper relation to each other, and transmit half of the power. Depending upon which of the two shafts 3, 4 is the drive shaft, one of these shafts terminates in the double outer bearing 46, while the other shaft continues through the double-outer bearing 46 upon which the pulley 48 is mounted; or

.delivery chamber 24. Unloading the drive may be connected to the driving shaft in any other suitable means. The double outer bearing 46 is mounted upon the pedestal 47 which, together with the head plate sections 38, 39 and the cylinder sections 9, 11 at the feet 17, 18 are preferably mounted upon the one piece bed plate 44 forming I comprises one embodiment of my unloading means. The check valve body 49 contains the valves 52, 53 disposed within the valve .bonnets 54 55, for the purpose of preventing a return flow of the medium through the ports 56, 57, under the valves 52, 53, into the is accomplished automatically by a fluid pressure motor comprising preferably a pressure regulated pilot valve which. controls the inflow,

'the opening 103' of the upper valve be and outflow of the medium at the discharge or delivery pressure, and which also controls the alternate inflow and outflow of the mepositions.

dium at the suction pressure, thus actuating a by-pass valve to full open or to full shut When this by-pass valve is in its full shut position, none of the medium can return to the suction side. When unloaded, this by-pass valve is in its full open position and none of the medium is'delivered into the discharge line, the check valve 49 preventing any return from the discharge P P The pilot valve body 58 is shown ,in one embodiment of my invention and comprising the pilot valve 59, having the cut away ports 60, and further having its valve stem 61 connected to the. diaphragm 62 by the plate 63 and the nut 64, all disposed wlthin the body 58. The diaphragm 62 is also held .to' the valve stem 61 by the plate 65 and the nut 66. The valve stem 61 is connected by the link 67 with the lever 68' and the pin 69. The lever 68 has its fulcrum on the pin 70, supported by the bracket 71. The bracket 71 is mountedon the top of the body section 72.

The diaphragm 62- is held in place by the body section 72. The lever 68 may be connected with a dash pot 73 by the link 74 and the pin 75. The weights 76, supported by the rod 77, attached to the lever 68 may be va ried to balance thediaphragm action at any desired ressure with. the aid of the slide weight 8 which may be set at'diflerent posi-, tions on the lever 68. The lever 68 is limited in its movement up and down by the slotted stop 7 9 disposed around the lever 68 and mounted upon the body section 7 2. The top of the diaphragm 62 is subjected to atmospheric pressure through the opening in the body 72.

The pipe 81 .connects the discharge pipe side of the check valve body 49 with the T 82 and with the T 83. The body 58 is connected with the discharge pipe by the pipe 84 and thepip'e 85 at 86 from the Ts 82 and 83, thus subjecting the lower side of the pilot valve 59 and the lower side of the diaphragm 62 to the discharge pressure. The valve body 58 has the port 87, connected by the pipe 89 and the T 83 with the discharge pressure through the pipe 81. The Valve body 58 also has the spaced ports 90 and 91,

both communicating with their cut away ports 60 of the pilot valve 59 when the pilot, valve 59 is in its bottom position as shown, which occurs when the pressure in the discharge pipe is insuflicient to raise the diaphragm 62 connected with the pilot valve 59-. The by-pass valve 92, disposed within the valve body 93 is connected with the diaphragm 94, and is held in place by the upper valve body section 95, by'the valve stem 96, the nuts 97, 98, the plate 99, the nut 100, the plate 101, the nut 102, and extends through 3 section 95 where the shelf 104 is attached to the valve stem '96 by the pin 105. The

weights 106 are placed upon the shelf 104 in the required number'and size to insure the return of the by-pass valve 92 to its seat 107 when the pressure under the diaphragm 94 within the valve body 93 is the same as the suction pressure of the medium being pumped or compressed.

The valve body 93 having the ports 108, is connected by the pipe 109 with the discharge chamber 24 at the flange 37, and also, the valve body 93 is connected by the pipe 110, the T 111 of the suction main, the pipe 112, the elbow 113 to the pipe plate 114 at the suction side of the machine. The space be-' tween the diaphragm 94 and the valve body sis 93 is.connected with the port 90 of the pilot valve body 58 by the pipe 115. The port 91 of the valve body 58 is connected with the suction pipe by the pipe 116. Thus, it will be noted that during periods when the discharge pipe pressure is insufficient to raise port 87 will be closed from thedischar e together through the cut away port 60 of the the diaphragm 62 and the pilot valve 59, the

pilot valve 59, the result being that the suction pressure will operate against the bottom of the diaphra 94,through the pipes 115, 116, and the orce of the suction ressure operating over the diaphragm 94 wi 1 be insuflicient to lift the valve stem 96 and the weights 106,-and the by-pass valve 92 will be held on its seat 107, and as the by -pass valve ports 108 will be closed, no gas or medium being pumped or compressed can by-pass, and the machine will deliver its full capacity into the discharge, and unloading will be entirely inefiective.

When an excess quantity of the medium is delivered by the machine into the discharge,

, pipe 81 will be opened, the port 90 will remain open, and the pressure under the diaphragm 9 L will have been changed from suction pressure to discharge pressure, the weights 106 will be insufiicient to hold the valve stem 96 down, and the by-pass valve 92 will become fully opened. The medium in the discharge pipe is prevented from returning through the closing of the check valves 52, 53, the discharge chamber 24 is connected with the suction 114 through the pipe 109, the open port 108, the pipes 110, 111, 112 and 113,-there will be no increase in the pressure of the medium as it passes through the machine, the medium merely being recirculated at suction pressure requiring only suflicient power for driving to overcome the friction of the machine, and unloading is fully eflective.

As soon as withdrawals from the discharge line reduce the pressure under the diaphragm 62 sufiiciently, the pilot valve 59 will return to the position shown, the pressure under the diaphragm 94; will again become the suction line pressure, the by-pass valve 92 will fully close, and no by-passing takes place. All of the medium which passes through the machine is delivered into the discharge pipe, and unloading will again be entirely inefi'ective, the alternate loading and unloading periodically becoming effective to maintain a substantially constant delivery .line pressure, and reduction in power consumption in substantial proportion to the quantity of the medium delivered into the discharge pipe.

It will be understood by those skilled in the art, that the pilot valve means and the lay-pass valve means illustrated in the drawmgs may be rearranged and modified to be responsive to any desired vacua in lieu of pressure. Also, in certain applications it may be preferable to have the pilot valve means, or the by-pass valve means, or both operated or controlled electrically, hydraulically, or pneumatically, either separately or in combination as desired. 7 Though I have described valve means for preventing instantaneous compression, it will be understood that in extremely high speed machines with a large number of deliveries into the discharge per unit of time, the return flow of the gas into the compression compartments may be prevented by omitting the valves and restricting the port openings at the discharge side to an extent which will produce a movement of the gas solely in one direction.

It will be observed that myinvention provides for the discharge of the compressor into the discharge line under. conditions of pressure inthe discharge line not exceeding any predetermined value, under which condition the by-pass between the discharge and inlet openings is closed; further, under the condition of the pressure in the discharge line exceeding such predetermined value, the discharge from the compressor is by-passed back to the inlet of the compressor. Preferably, as is illustrated and described hereinabove, the valve controlling m by-pass assumes in this operation either a ully open position or a fully closed position, in which event the discharge from the compressor is wholly prevented from going into the discharge line and is led back through the open y-pass valve to the inlet of the compressor.

Whereas, I have described my invention by reference to specific forms thereof, it'will be understood that many changes and modifications may be made without departing from the spirit of the invention.

I claim: I

1. The combination of a casing having an inlet and a discharge, said inlet being free of any valve, means including impellers disposed within said casing for compressin a fluid, driving means for said impellers, va ve means for said discharge, fluid passage means communicating at its one end with said discharge of said casing between said valve means and said impellers and at its opposite end with said inlet for controlling the discharge through said discharge valve means, said fluid passage means including a valve responsive to discharge and inlet pressures and movable solely to fully o ened and fully closed positions, and means or moving. said valve solely to fully opened and fully closed positions.

2. The combination of a casing having an inlet and a discharge, said inlet being free of any valve, means including impellers disposed within said casing for compressing a fluid, driving means for said impellers, valve meansfor said discharge, fluid passage means communicating at its one end with said discharge of said casing between said valve means and said impellers and at its opposite end with said inlet for controlling the discharge through said discharge valve means,

said discharge controlling means including I moving said valve solely to fully opened and fully closed positions.

3. The combination of a casing having an inlet and a discharge, said inlet being free means and said impellers and at its opposite-.

end with said inlet for controlling the discharge through said discharge valve means, said vdischarge controlling means including a manually variable weight adjustable valve, responsive to inlet and discharge pressures and movable solely to fully o ened and fully closed positions, and means or moving said valve solely to fully opened and fully closed positions.

4. The combination of a casing having an inlet and a discharge, said inlet being free of any valve, means including impellers disposed within said casing for compressing a fluid, driving means for the impellers, valve means for said discharge, and'fluid passage means communicating at its one end with said discharge of said, casing between said valve means and said impellers and at its opposite end with said inlet for controlling the discharge through said discharge valve means, said discharge controlling means including a evice responsive'to the pressure at the inlet and the discharge of said casing.

5. The combination of a casing having an inlet and a discharge, said inlet being free of any valve,means including impellers disposed within said casing for compressing a fluid, driving means for the impellers, valve means for said discharge, a delivery llne sage means communicating at its one end withsaid discharge of said casing between said valve means and said impellers and at its op osite end with said inlet for controlling t e discharge through said discharge valve means, said discharge controllingmeans including a valve responsive to the pressure of said inlet and said delivery line.

6. The combination of a casing having an inlet and a discharge, said inlet being free of any valve, means including impellers dis-' posed within said casing for compressing the fluid, driving means for the impellers, valve means for said discharge, a delivery line communicating with said discharge through said discharge valve means, and fluid passage means communicating at its one end with said discharge between said discharge valve means and said impellers and'at its opposite end with said inlet for controlling the discharge through said discharge valve means, said discharge controlling means includinga valve responsive jointly to the pressure in said discharge line and the pressure at said inlet.

7. The combination of a casing having an inlet and a discharge, means disposed within said casing for compressing a fluid, drivng means, check valve meansforsaid .dis-

charge, check valve means disposed in the discharge of said casing anteriorly of said first named discharge valve means, and means communicating at its one end at a location-intermediate said first named and said second named discharge valve means and at its other end with said inlet for controlling the discharge of compressed fluid through said first named discharge valve means.

8. The combination of a casing having an inletand a discharge, meansdisposed with in said casing for compressing a fluid, driving means, check valve means for Stud discharge, check valve means disposed in the discharge of said casing anteriorly of said first named discharge valve means, and means communlcating at its oneend at a location intermedlate said first named and said second named discharge valve means and at its other end with said inlet for controlling the discharge of compressed fluid through said first named discharge valve means, said discharge controlling means including a pressure responsive device.

9. The combination of a casing having an inlet and a discharge, means disposed with in said casing for compressing a fluid, driving means, check valve means for said discharge, check valve means disposed in the discharge of said casing anterlorly of said first named discharge valve means, and

means' communicating at its one end at a location intermediate said first named and said second named discharge valve means a and at its other end with said inlet for controlling the discharge of compressed fluid through said first named discharge valve means, said discharge controlling means including a manually variable weight adjustable valve.

10 The combination of a casing having an inlet and a discharge, means disposed within said casing for compressing a fluid,

driving means, check valve means for-said.

discharge, check valve means disposed in the discharge of said casing anteriorly of said first named discharge valve means, andv means communicating at its one end at a location intermediate said first named and said second named discharge valve means and at its other end with said inlet for controlling the discharge of compressed fluid through said first named discharge valve means, said discharge controlling means including a device responsive to the pressure at the inlet of said casing.

,11; The combination of a casing havin an inlet and a discharge, means disposed within said casing for compressing a fluid, driv ing means, check valve means for said discharge, a delivery line communicating with said discharge through said discharge valve means, check valve means disposed in the discharge of said casing anteriorly of said first named discharge valve means, and means communicating at its one end to a location intermediate said first named and said second named discharge valve means and at its other end with said inlet for controlling the discharge of compressed fluid through said first named discharge valve means, said discharge controlling mcans including a valve responsive to the pressure of said delivery line.

12. The combination of a casing having an inlet and a discharge, means disposed within said casing for compressing a fluid, driving means, check valve means for said discharge, a delivery line communicating with said discharge through said discharge valve means, check valve means disposed in the discharge of said casing anteriorly of said first named discharge valve means, and means communicating at its one end at a location intermediate said first named and said second named discharge valve means and at its other end with said inlet for controlling the discharge of compressed fluid through said first named discharge means, said discharge controlling means including .a valve responsive jointly to the pressure in said discharge line and the pressure at said inlet.

13. The combination of a casing, an impeller disposed within said casing for compressing a fluid, driving means for said impeller, discharge and inlet piping for said casing, passage means closed to-the atmosphere interconnecting said discharge and inlet piping, a power operated valve for said passage means, a unidirectional valve for said discharge piping and means responsive to the pressure of said discharge piping and said inlet piping for controlling said passage means valve.

14. The combination with a compressor providedwith inlet and discharge openings,

and a discharge line, of means for controlling the discharge of fluid from said compressor into said discharge line, said controlling means comprising by-pass means communicating at one end with said discharge opening and at its opposite end with said inlet opening, a valve controlling said by-pass means and pilot valve means controlled by the pressure in said discharge line for operating said valvemeans alternately to fully open and fully. closed positions.

15. The combination with a compressor provided with inlet and discharge openings,

and a discharge line, of means for controlling thedischarge of fluid from said com: pressor into said discharge line, said controlling means comprising by-pass means communicating at one end with said discharge opening and at its opposite end with said inlet opening, a valve controlling said by-pass means and power operated pilot valve means controlled by the pressure in said discharge line for operating said valve means alternately to fully open and fully closed positions.

16. The combination with a compressor provided with inlet and discharge openings, and a discharge line, of means for controlling the discharge of fluid from said compressor into said discharge line, said controlling means comprising by-pass means communicating at one end with said discharge open-- ing and at its opposite end with said inlet opening, a valve controlling said by-pass means and valve means controlled by the pressure in said discharge line for operating said valve controlling said by-pass means alternately to fully open and fully closed positions, said valve means comprising a pilot valve member, a casing enclosing said pilot valve member and provided with a port, and a piping connecting said port with said discharge line.

17. The combination with a compressor provided with inlet'and discharge openings, and a discharge line, of means for controlling the discharge of fluid from said compressor into said discharge line, said controlling means comprising by-pass means communicating at one end with said discharge opening and at its opposite end with said inlet opening, a valve controlling said by-pass means and valve means controlled by the pressure in said discharge line for operating said valve controlling said by-pass means alternately to fully open and fully closed positions, said valve means comprising a pilot valve member, a casing enclosing said pilot valve member and provided with a plurality of ports and piping respectively connecting said ports with said discharge line and said inlet opening.

18. The combination with a compressor provided with inlet anddischarge openings, and a discharge line, of means for controlling the discharge offiuid from said compressor into said discharge line, said controlling means comprising by-pass, means communieating at one end with said discharge opening and at its'opposite end with said inlet opening, a valve controlling said by-pass means and valve means controlled by the pressure in said discharge line for operating said valve controlling said by-pass means alternately to fully open and fully closed positions, said valve means comprising a pilot valve member, a casing enclosing said pilot valve member and provided with a port, an? piping connecting said port with said inl t opening. r l

19. The combination with a compressor provided with inlet and discharge openings,

and a discharge line, of means for controlling the discharge of fluid from said compressor into said discharge line, said controlling means comprisin by-pass means communieating at one 'en with said discharge 0 ning and at its opposite end with said 1nlet opening, a valve controlling said by-pass means and valve means controlled by. the pressure in said discharge line for operating said valve controlling said b -pass means alternately to fully open an fully closed positions, said valve means comprising a pilot valve member, a casing enclosing said pilot valve member andprovided with a port at which the pressure is maintained the same as that of said inlet opening.

In testimony whereof "I have signed this specification this 10th day of September 1927.

EVERETT W. SWARTWOUT. 

